An exhaust and drain valve for a fuel cell 55 used in a fuel cell system disclosed in Japanese Patent No. 5948792 (Reference 1) is disposed in a fuel system discharge pipe 51b which discharges a fuel off gas or water caused by electric power generation of a fuel cell 6 to the outside, as illustrated in FIG. 1 of Reference 1. Discharging the fuel off gas or the like to the outside is allowed or blocked by opening and closing the exhaust and drain valve for a fuel cell 55. In addition, the exhaust and drain valve for a fuel cell 55 is a diaphragm valve in which a diaphragm is used, as illustrated in FIG. 2 of Reference 1.
In the above-described fuel cell system 1 disclosed in Reference 1, a substance that causes pressure loss in a fluid may be disposed in a portion of the secondary side of the exhaust and drain valve 55 in the fuel system discharge pipe 51b. For example, a fuel cell system of Reference 1 is used for vehicles, and thus a muffler or the like equipped with a filter is disposed in the fuel system discharge pipe 51b. In this case, the pressure in the portion of the secondary side of the exhaust and drain valve 55 in the fuel system discharge pipe 51b is increased as compared with a case where the muffler or the like is not disposed, and thus a force pressing one side surface (a lower side surface) of a diaphragm portion 97b is increased so as to switch the exhaust and drain valve 55 from a closed state to an open state. In contrast, the other side surface (an upper side surface) of the diaphragm portion 97b is open to the atmosphere, and thus the pressure pressing the other side surface of the diaphragm portion 97b so as to switch the exhaust and drain valve 55 from the open state to the closed state is constant at an atmospheric pressure. Thus, in this case, the sealability of the exhaust and drain valve 55 is considered to be decreased.
Thus, a need exists for a fuel cell system which is not susceptible to the drawback mentioned above.